a. Field of Invention
The present invention relates to generating rocket motor burnback data, pressure versus time, and thrust versus time data for various firing temperatures, using generally available specifications of the rocket motor and test firing data.
b. Background
In order to simulate the ballistics performance of a particular rocket motor, it is necessary to have a burnback profile. A burnback profile is developed by plotting the burn surface area as a function of the linear web burned. FIGS. 7, 9, 11 and 13 are examples of burnback profiles. The area under the curve equals the volume of propellant burned. The curve is unique for each different rocket motor and is a function of the geometry of the propellant grain. The burnback profiles are generally available only to those personnel intimately familiar with the design and development of the motor. Even when such detailed information is available, correction factors which are often unique for a given temperature must be applied to produce a valid model of ballistics performance. Test data from actual firings can be used to plot the curve and produce a burnback profile but rocket motors are normally tested at extreme temperatures only and actual firing test data is generally not available for temperatures within the normal range of use, for the rocket motor. It would be expensive and impractical to conduct a series of test firings, for each rocket motor, in order to obtain representative data for a spectrum of temperatures, so that curves could be generated from the data, for representative firing temperatures.
Computer models have been developed to take advantage of the available test data, for firings at extreme temperatures, and to produce a predicted curve. U.S. Pat. No. 6,290,505 to Garcia-uses a thrust versus time curve from a test firing and proportionally expands or contracts the base line to an interpolated ending point for a temperature, for which the data is to be modeled. A computer program produces a thrust-time curve having the same basic shape and equivalent impulse (area under the curve). The interpolation approach used in the Garcia '505 patent is more of a graphical re-proportioning of the thrust-time curve.
There remains a need for a method and a computer model which can mathematically develop an accurate curve and data profiles for a temperature different from those temperatures for which firing test data is available.